Mine prop jack and method of prestressing a mine prop

ABSTRACT

A telescoping mine prop is prestressed by engaging the prop with a jack and thereby telescopically expanding the prop against opposing surfaces of the mine with the jack. Thereafter the prop is locked in position and the jack is disengaged from the prop for use with the expansion of another prop, thereby leaving the mine prop in a prestressed condition.

BACKGROUND OF THE INVENTION

The present invention relates generally to mine roof control, and more specifically, is directed to prestressing a standing support referred to as a mine prop. Such roof supports are useful in areas where mine roof bolting machines are not practical or the roof pressure is too great for conventional roof bolts.

As mining conditions continue to deteriorate due to depletion of easily accessible reserves, greater rock loads from increasing overburden are becoming the norm in mining. In order to protect miners from roof falls the root support or mine prop is prestressed so that the immediate strata does not have the opportunity to begin convergence. Controlling the initial convergence of the strata is critical in roof conditions that have a high degree of creep. Currently there are two methods of prestressing a standing support. One is accomplished with inflatable metal bladders that require a water reservoir and a pump. The second method involves pumping mortar into a bag on top of the support. The negative points with inflatable metal bladders are that a large reservoir of water must be transported to the work site and the maximum extension possible with a metal bladder is four inches. Another problem incurred with the mortar bag is that the mortar has a setting time of several hours.

It is therefore an object of the present invention is to provide a jack mechanism for a mine prop which allows the miner flexibility in the installation process and which is light enough to be carried by one person and also provides immediate prestressing of the mine prop.

SUMMARY OF THE INVENTION

The mine prop jack of the present invention is provided for prestressing a telescopically expandable mine prop which has a head plate and a foot plate secured to opposite ends and also includes a lock for adjustably locking the mine prop in an expanded condition. The present invention provides an expandable jack post which is deposed between the head and foot plate of the mine prop for expanding the prop against opposing surfaces (mine roof and floor) to a condition of prestress after engaging the mine prop lock and releasing the jack post. The jack post is temporarily tied to the mine prop to maintain the jack post in position during the operation. The jack post is then disengaged from the mine prop and moved to the next site where it is secured to another mine prop for conducting the prestressing operation over again.

Positive prestressing of the support is provided with the apparatus and method of the present invention. The jack mechanism can be carried by one person and attached and operated with no tools required and the requirement for water and cement is eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages appear hereinafter in the following description and claims. The accompanying drawings show, for the purpose of exemplification, without limiting the scope of the present invention or the appended claims, certain practical embodiments of the present invention wherein:

FIG. 1 is a schematic representation in front elevation of the jack of the present invention, with a mid portion thereof sectioned away to expose the interior, shown in combination with a telescoping mine prop to be prestressed;

FIG. 2 is a left side view of the combination shown in FIG. 1; and

FIG. 3 is a right side view of the combination shown in FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to the drawings, the telescopically expandable mine prop 10 includes a lower pipe section 11 which telescopically or slidably receives therein upper pipe section 12. Head plate 13 and foot plate 14 are welded to opposite ends of the prop 10 and the prop 10 is thus expandable such that head plate 13 and foot plate 14 respectively engage the mine roof 15 and mine floor 16. A vertical series of apertures 17 are provided in the mine prop 10 in order to receive a lock pin therein to permit preliminary adjustable locking of the mine prop 10 prior to full expansion for prestressing and subsequent locking of the prop 10 after full expansion for prestressing.

Jack post 20 of the present invention includes upper and lower clamps 21 and 22 respectively which consist of spaced ears 23 that engage opposite sides of prop 10 and are retained in position temporarily by the placement of bolts 24 through aligned apertures provided in the spaced ears 23. This retains jack post 10 in position with the upper and lower ends 25 and 26 respectively engaged against the inside surfaces of head and foot plate 13 and 14.

Upper pipe extension 27 is telescopically received over lower pipe extension 28 and upper pipe extension 27 may be raised or lowered relative to lower pipe extension 28 so that the jack 20 may be initially extended or expanded until the upper end 25 thereof engages the underside of head plate 13.

The small mid portion of jack 20 is broken away in FIG. 1 to expose an interior of lower pipe sleeve 28 and the upper end 29 of the jack piston for hydraulic jack 30. The lower end 31 of jack 30 rests against base plate 32 that is welded to the upper end of pipe base 33.

Hydraulic jack 30 is a conventional hand operated hydraulic jack that may be readily purchased in the market and is hand operated by pumping jack lever 34.

A vertical series of apertures 35 are provided in the upper pipe extension 27 so that the jack post 20 may be initially positioned and expanded between head and foot plates 13 and 14 and there temporarily held in position by inserting a lock pin in the appropriate aperture 35 for initial pre-positioning of the jack post 20.

Once jack post 20 is attached as described to prop 10 and initially expanded for initial engagement between head and foot plates 13 and 14, then hydraulic jack 30 is operated by pumping handle 34 to expand jack post 20 into engagement with upper end 25 and lower end 26 thereof against the inside of head plate 13 and foot plate 14 in order to provide a maximum expansion under load of the mine prop 10.

When this has been attained, prop 10 is locked in position by inserting locking pins in one or more apertures 17, and jack post 20 is disengaged from prop 10 thereby leaving mine prop 10 in a prestressed condition. Jack post 20 is disengaged by relieving the hydraulic pressure within jack 30 and thereafter removing pins 24 to remove the entire jack post 20 from prop 10 so that the operator may then carry the jack post 20 to the next location for prestressing the next mine prop 10. 

1. A mine prop prestressing device comprising; a jack having means for temporarily attaching it to a telescoping mine prop for expanding said prop into prestressed engagement with opposing surfaces.
 2. The mine prop of claim 1, wherein said jack consists of a jack post which is expandable against opposing head and foot plates secured to opposite ends of said mine prop for expanding said mine prop with said jack post.
 3. The mine prop of claim 2, wherein said jack post is a telescopically expandable post having a hand operated hydraulic jack disposed therein.
 4. The mine prop of claim 2, said means for temporarily attaching including upper and lower clamps for temporarily clamping said jack post to said mine prop.
 5. A combination mine prop and jack for prestressing the mine prop, comprising: a telescopically expandable mine prop having a head plate and a foot plate secured to opposite ends; a lock for adjustably locking said prop in an expanded condition; an expandable jack post disposed between said head and foot plates for expanding said prop against opposing surfaces to a condition of prestress after engaging said lock and releasing said jack post; and tie means temporarily tying said jack post to said mine prop.
 6. The combination of claim 5, wherein said jack post includes a hand operated hydraulic jack.
 7. The combination of claim 5, said lock consisting of a longitudinal series of apertures in one portion of said telescopically expandable mine prop which is telescopically movable relative to a second part thereof, and a pin receivable in one of said apertures and engageable with said second part to lock said prop in an expanded prestressed condition.
 8. The combination of claim 5, said tie means including upper and lower clamps for temporarily clamping said jack post to said mine prop.
 9. The method of prestressing a telescoping mine prop comprising; engaging said prop with a jack; telescopically expanding said prop against opposing surfaces with said jack; locking said prop at its expanded position; and disengaging said jack from said prop for use with the expansion of another prop and thereby leaving said mine prop in a prestressed condition. 